Water Supply information

There are several key parts to a typical water supply. These include: source, well-head or bore-head, storage tank(s), filtration, water treatment, reticulation and backflow prevention.

Water sources

Selwyn water supplies generally draw water from the following two sources:

  1. Ground water (aquifers):
    1. Deep secure ground water. These sources are protected from the influence of surface water contamination and are usually deemed to better source of raw water supply.
    2. Shallow or insecure ground water. Shallow bores and wells are generally at a higher risk of contamination and may require a higher level of treatment.
  2. Surface water (general)
    1. Sourced from rivers, streams, creeks, water races and irrigation races. These open catchment sources are at higher risk of contamination and need higher levels of treatment before distribution.

Well-head or bore-head protection

The well-head or bore-head is where the water is extracted from the ground. It should comprise of a suitably designed and constructed concrete pad and has to be well sealed. This protects the bore and prevents any contamination from the surface, e.g. during surface flooding or heavy rainfall periods.

Water filtration and treatment

Water from non-secure ground water (shallow bores or wells), and surface water is treated under most circumstances. Treatment involves mostly filtration and disinfection. Filtration removes suspended matter (particles) from the water and this enables effective water treatment to remove harmful microorganisms such as bacteria (e.g. E.coli) and protozoa (e.g. Cryptosporidium and Giardia).

There are various types of filtration. These include cartridges, filter bags, candle filters, sand filters and reverse osmosis. Selwyn has many supplies with cartridge micron filters that have proven to be an effective medium to maintain a good quality water for an advance level of treatment.  There are various methods of water treatment. These include: Ultra Violet Light sterilisation, chlorination and ozone. The main method is UV light. Treatment systems such as UV light need to be of a suitable design and well-maintained. Selwyn has 13 supplies which have a state of art validated UV treatment system.

Whilst UV treatment system ensures that the Water is disinfected at the treatment plant, there is still the possibility of contamination from infiltration on the pipes or other factors. Therefore some level of residual disinfection is required in the reticulation network. Chlorine is added in the water to achieve this end result from time to time. Surface water supplies like Acheron, Malvern Hills Dalethorpe, and Springfield & Hororata have chlorination as an additional protection barrier.

Storage tanks in Restricted Water Schemes

Many properties, particularly in the rural zones, are required to have water storage tanks. These tanks store water for sustainability for domestic use and fire-fighting purposes.  It’s important that tanks are well-sealed to prevent the entry of birds, feral animals, rodents and insects from entering the tank and contaminating the water. Cracks around the top and unsealed lids need to be sealed. Breather holes need to be screened for insects.

View guidelines and instructions on how to Disinfect Water Storage Tanks [PDF, 129 KB]

Backflow protection

Backflow prevention is important, particularly on farms and on properties where commercial or industrial activities are being undertaken. Backflow prevention ensures that no contamination is able to backflow into the water source or the reticulation. There are different methods of backflow prevention. Examples are: air gap separation by ball cock, a range of back flow prevention devices depending on the water pressure and purpose. Back flow prevention systems and devices need to be maintained to ensure they are fully operational and effective.

More information about Backflow prevention

Useful Links

Some helpful external links for further information